Morton's Neuroma

Morton's Neuroma (interdigital neuroma, Morton's metatarsalgia) is a common cause of forefoot pain representing compression neuropathy of the common digital nerve.

Terminology

• Misnomer: Not a true neuroma (not neoplastic)
• Correct Term: Interdigital nerve compression or perineural fibrosis
• Historical: Named after Thomas Morton (1876), though Durlacher described it earlier (1845)

Epidemiology

• Prevalence: 30% of patients with forefoot pain
• Gender: Female predominance 8:1 (high heels, narrow shoes)
• Age: 4th-6th decade most common
• Bilateral: 15-20% bilateral involvement

Web Space Distribution

• 3rd Web: 65% (between 3rd and 4th metatarsals) - MOST COMMON
• 2nd Web: 30% (between 2nd and 3rd metatarsals)
• 4th Web: 3% (rare)
• 1st Web: 2% (very rare)
• Multiple: 2-3% have involvement of more than one web space

Why 3rd Web Most Common?

• Junction of medial and lateral plantar nerve branches
• Nerve thicker at this level
• More tethered → less mobile → more susceptible to compression

Relevant Anatomy

Pathophysiology

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Risk Factors

• Footwear: High heels (transfers weight forward), narrow toe box
• Foot Type: Pes planus, hypermobile first ray
• Activities: Running, ballet, activities with repetitive forefoot loading
• Anatomical: Long metatarsals, tight intermetatarsal space

History

Physical Examination

Mulder's Test (Key Examination)

Web Space Compression Test

• Direct pressure on affected web space (plantar and dorsal)
• Reproduces symptoms
• Less specific than Mulder's

Sensory Examination

• May have decreased sensation in adjacent toes
• Two-point discrimination may be abnormal
• Often normal early in disease

Clinical Diagnosis

• Diagnosis is primarily CLINICAL
• Imaging not always required if classic presentation
• Used to confirm diagnosis or exclude other pathology

Ultrasound

MRI

Diagnostic Injection

• Local anaesthetic injection into web space
• Relief confirms diagnosis
• Can be combined with corticosteroid for treatment

Surgical Complications

Global Epidemiology

• One of the commonest causes of forefoot neuralgia worldwide; strongly associated with constrictive footwear and elevated heels
• Marked female predominance (commonly quoted around 8:1) across populations; peak in the 4th-6th decades
• 3rd web space dominates, followed by the 2nd; multiple/bilateral involvement in a minority
• Lower reported prevalence in habitually barefoot or wide-footwear populations, supporting a footwear-driven mechanical aetiology

Guidelines & Society Positions (Side by Side)

Registry & Evidence Notes

• No dedicated implant registry applies (no implant is used); evidence is driven by RCTs (steroid injection) and surgical case series rather than arthroplasty-style registries
• Imaging meta-analysis confirms ultrasound is equivalent to MRI for detection and is the more cost-effective first-line test
• Economic modelling supports an injection-first pathway (steroid then alcohol) before surgery when conservative measures fail

High- vs Limited-Resource Practice Variation

• Well-resourced settings: ultrasound-guided diagnosis and injection, day-case dorsal neurectomy, MRI for atypical/recurrent cases
• Limited-resource settings: clinical diagnosis with Mulder's sign and footwear/padding emphasised; diagnostic local-anaesthetic injection substitutes for advanced imaging; surgery reserved for refractory disease
• Workforce: depending on jurisdiction, surgery is performed by orthopaedic foot-and-ankle surgeons or, where licensed, podiatric surgeons; complex/revision cases are typically referred to specialist foot-and-ankle units

Multiple Neuromas

• 2-3% have multiple web space involvement
• MRI helpful for preoperative planning
• May require staged surgery
• Higher risk of complications

Recurrent Morton's Neuroma

Differential Diagnosis

• Metatarsalgia: Pain under metatarsal heads, no radiation
• Stress Fracture: Point tenderness over bone, swelling
• MTP Synovitis: Joint swelling, positive Drawer test
• Freiberg's Disease: 2nd MT head AVN, adolescent female
• Plantar Plate Injury: MTP instability, Drawer positive
• Peripheral Neuropathy: Multiple toes, bilateral

The topic repeatedly names alcohol sclerosing injection, radiofrequency ablation and cryoneurolysis as non-operative alternatives without developing them. These are targeted nerve-ablation techniques positioned between corticosteroid injection and open neurectomy — for patients who have failed footwear and steroid but wish to avoid surgery and its expected numbness.

Alcohol (Ethanol) Sclerosing Injection

• Principle: Dilute ethanol is neurotoxic — it produces chemical (Wallerian) degeneration of the common digital nerve, effectively a "chemical neurectomy" without an incision.
• Technique: Ultrasound-guided injection of dilute ethanol (commonly around 20-30% ethanol mixed with local anaesthetic) into the web space around the neuroma, repeated as a series (often several injections at one-to-two-week intervals).
• Evidence: Case series report widely varying success (roughly 60-90% symptom relief), but the systematic review by Matthews et al judged sclerosing-injection studies to be of limited methodological quality, and durable high-level RCT evidence is lacking.
• Cautions: Extravasation of alcohol can cause skin necrosis, plantar fat-pad injury or local reactions; incomplete response and symptom recurrence are common.

Radiofrequency Ablation & Cryoneurolysis

• Radiofrequency ablation: Thermal lesioning of the nerve under image guidance; reported in small case series with promising short-term relief.
• Cryoneurolysis: Freezing (cryoablation) of the nerve to interrupt conduction; also limited to case-series evidence.
• Status: Both are minimally invasive, sensation-preserving in intent and repeatable, but neither has robust randomised support — they remain second-line options where surgery is declined or high-risk.

Where They Fit

• A reasonable trial after failed footwear/pad and steroid, before open surgery — supported by cost-effectiveness modelling (Ross et al) showing a sequential steroid-then-alcohol injection pathway can be the dominant strategy.
• Not a substitute for accurate diagnosis: confirm the lesion on ultrasound and exclude adjacent-space or alternative pathology first.

The Controversies section raises "neurectomy versus nerve-preserving surgery" but never explains the decompression option. Decompression (neurolysis) treats Morton's neuroma as an entrapment rather than a mass — the deep transverse intermetatarsal ligament is divided to relieve compression while the nerve is left in continuity, preserving sensation and avoiding a stump neuroma.

Rationale

• Morton's neuroma is fundamentally a compressive neuropathy beneath the transverse metatarsal ligament, so releasing that ligament addresses the cause without sacrificing the nerve.
• Gauthier popularised isolated division of the transverse intermetatarsal ligament (decompression) as a nerve-sparing alternative to excision.

Techniques

• Open decompression / neurolysis: Dorsal incision, division of the transverse intermetatarsal ligament and external neurolysis of the common digital nerve; the nerve is preserved.
• Endoscopic decompression of the intermetatarsal nerve (EDIN): A minimally invasive endoscopic release of the ligament, aiming for quicker recovery and a smaller scar.

Trade-offs vs Neurectomy

• Advantages: Preserves toe sensation (no expected numbness), avoids stump neuroma, and if it fails, neurectomy remains available as a salvage.
• Disadvantages: Higher risk of incomplete relief and recurrence because the pathological nerve is left in situ; best suited to earlier disease or smaller lesions where fibrosis is limited.
• Selection: Larger, chronically fibrotic neuromas and clear mass lesions are generally better served by excision; decompression is attractive when sensation preservation is the priority.

• Does corticosteroid add anything over local anaesthetic? The 2013 Edinburgh RCT (Thomson) showed benefit over placebo, but the 2017 double-blind RCT (Lizano-Diez) found steroid no better than anaesthetic alone — the durable advantage of the steroid component remains contested.
• Neurectomy vs nerve-preserving surgery. Decompression (transverse intermetatarsal ligament release) avoids permanent numbness and stump neuroma but carries a higher recurrence risk; excision sacrifices sensation but is more definitive. The optimal choice is unsettled and patient-specific.
• Dorsal vs plantar incision. The dorsal approach avoids a weight-bearing scar and allows earlier mobilisation; the plantar approach gives superior exposure and, when correctly placed, a low scar-problem rate. High-level comparative evidence is lacking — largely surgeon preference.
• Size threshold for significance. A commonly cited cut-off is greater than 5mm, but symptoms correlate imperfectly with size and asymptomatic lesions are seen on imaging — imaging should confirm, not drive, the diagnosis.
• Minimally invasive alternatives. Alcohol sclerosing injection, radiofrequency ablation and cryoneurolysis show promise in case series but lack robust RCT support; reported success rates vary widely and reflect heterogeneous protocols.
• Bursa vs nerve. Whether the dominant pain generator is perineural fibrosis or an associated intermetatarsal bursitis is debated, which partly explains variable response to injection placement.

Morton's neuroma is a compressive neuropathy of the common digital nerve, most commonly affecting the 3rd web space (65%), not the 2nd. It is NOT a true neuroma but rather perineural fibrosis from repetitive compression beneath the transverse metatarsal ligament, with an 8:1 female predominance. Patients report burning, shooting pain radiating to adjacent toes, often relieved by removing shoes. Mulder's click (palpable click with lateral metatarsal squeeze while pressing the web space) is pathognomonic. Conservative management (wide shoes, metatarsal pad, corticosteroid injection 30-40% response rate) is first-line. Surgical neurectomy (dorsal or plantar approach) achieves 80-85% good outcomes; permanent numbness between affected toes is expected and must be counseled. Stump neuroma (10-15%) is the most common surgical complication.